1. Field of the Invention
The present invention relates to a regenerative refrigerator.
2. Description of the Related Art
A displacer type regenerative refrigerator and a pulse tube refrigerator are known. Japanese Laid-open Patent Publication No. 2008-224161 discloses a displacer type regenerative refrigerator including a displacer in which a regenerative material is provided within a tubular portion and a moving mechanism which reciprocates the displacer in a cylinder. In such a displacer type regenerative refrigerator, cooling is generated by expanding a refrigerant gas in an expansion space while reciprocating the displacer in the cylinder. Further, for the pulse tube refrigerator, cooling is generated by expanding a refrigerant gas in an expansion space while reciprocating a gas-piston in a pulse tube. The cooling of the refrigerant gas generated in the expansion space is transmitted to a cooling stage to be a desired cryogenic while being regenerated in the regenerator to refrigerate or the like an object to be cooled connected to the cooling stage.
A material having a larger specific heat capacity at a temperature inside the regenerator is used as the regenerative material. Japanese Laid-open Patent Publication No. H03-99162 discloses a structure in which a granular lead is used as a regenerative material and a granular magnetic material such as Er3Ni, EuS, GdRh or the like is used as a regenerative material at a lower temperature area.